How many headlights must function at all times according to Illinois law?

According to Illinois law, vehicles are required to have two headlights functioning at all times when on public roads. This requirement ensures that a vehicle is adequately visible to other drivers, particularly during low-light conditions or at night, thereby enhancing safety for both the driver and other road users. Having two headlights working allows for better illumination of the road ahead and aids in the visibility of the vehicle itself, which is crucial for preventing accidents.

The other options do not align with the legal requirements. For example, having only one headlight may provide some visibility but is not sufficient for ensuring full compliance with the law or for safe driving practices. Additionally, there is a specification for headlights to function at all times rather than during certain conditions, thus the notion of no specific requirement or varying numbers of headlights based on light conditions does not reflect the law accurately.